1. Field of the Invention
The present invention relates to a magnetic recording medium used in, for example, peripheral devices of calculators, or magnetic disk apparatuses used for recording of image and sound data, a process and apparatus for producing the magnetic recording medium, and a magnetic recording and reproducing apparatus incorporating the magnetic recording medium.
2. Description of the Related Art
As recording density of magnetic recording media is increased, reduction in noise and enhancement of resolution by means of miniaturization or magnetic isolation of magnetic grains in a magnetic layer, and or reduction of the thickness of the magnetic layer, for example, has been proposed.
However, when the magnetic grains are miniturized or magnetically isolated, or when thickness of the magnetic layer is reduced, the size of the magnetic grains is reduced, and therefore, there is a problem wherein thermal stability is decreased. The term xe2x80x9cthermal decayxe2x80x9d refers to a phenomenon in which recording bits become unstable and recorded data are lost. In a magnetic recording and reproducing apparatus, this is manifested in the form of reduction in reproduction output of recorded data over the passage of time.
Hitherto, as substrates used for magnetic recording media, non-magnetic metallic substrates comprising aluminum alloys and the like have been frequently used. Usually, a hard film comprising NiP or the like is provided on such a non-magnetic metallic substrate in order to harden its surface, then the surface of the substrate is subjected to texturing, and the substrate is used for producing a magnetic recording medium.
Texturing is a process for forming irregularities on the surface of a substrate along a predetermined direction (usually in a circumferential direction). By carrying out texturing, the crystal orientation of an undercoat layer and a magnetic layer, which are formed on the substrate, is enhanced, the magnetic anisotropy of the magnetic layer is enhanced, and magnetic characteristics, such as thermal stability, can be enhanced.
In recent years, instead of a metallic substrate comprising aluminum or the like, a non-metallic substrate comprising glass, ceramic, or the like has been widely used as a substrate for a magnetic recording medium. In the non-metallic substrate, head slap does not easily occur due to the high hardness, and furthermore, there is an advantage in the point of glide height characteristics because it has high surface smoothness.
In order to solve such problems, formation of a hard film which can be easily textured on a non-metallic substrate comprising glass, ceramics, or the like has been proposed.
For example, Japanese Unexamined Patent Application, First Publication No. Hei 5-197941 discloses a magnetic recording medium including a non-metallic substrate formed by sputtering with an NiP film which is a hard film that can be easily textured.
A magnetic recording medium including a hard film formed on a non-metallic substrate is produced through the following process: the hard film is formed on the substrate in a film formation apparatus such as a sputtering apparatus; thereafter, the substrate is temporarily removed from the film formation apparatus and subjected to texturing by use of a texturing apparatus; the resultant substrate is again placed in the film formation apparatus, and then an undercoat layer and a magnetic layer are formed.
However, in the case of the aforementioned conventional magnetic recording medium which uses a non-magnetic metallic substrate such as an aluminum substrate or a non-metallic substrate such as a glass substrate, when a hard film formed from NiP, which is formed on the surface, is subjected to texturing, the magnetic anisotropy of a magnetic layer can be enhanced but the surface smoothness of the medium tends to be lowered because of surface irregularities of the hard film. Consequently, glide height characteristics are deteriorated, and attainment of high recording density becomes difficult. In addition, the production process for the magnetic recording medium includes complicated production steps, resulting in high production costs.
The present invention was made in view of the foregoing conditions, and an object of the present invention is to provide: a magnetic recording medium which exhibits excellent magnetic characteristics such as thermal stability and excellent glide height characteristics and which is easily produced; a process and apparatus for producing the magnetic recording medium easily; and a magnetic recording and reproducing apparatus which uses the magnetic recording medium exhibiting excellent magnetic characteristics such as thermal stability.
The magnetic recording medium of the present invention has as a basic structure of a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein the non-magnetic undercoat layer has a bee structure; an orientation-adjustment layer for causing the non-magnetic undercoat layer to have a predominant plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; the magnetic layer has a crystal structure in which columnar fine crystal grains are inclined in the circumferential direction; the ratio of the coercive force in the circumferential direction of the magnetic layer Hcc to the coercive force in the radial direction of the magnetic layer Hcr, i.e., Hcc/Hcr, is more than 1.
The non-magnetic undercoat layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
The magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and a structure in which it is possible to form antiferromagnetic coupling between the magnetic films is preferable.
The orientation-adjustment layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
Due to the above constitution, the magnetic anisotropy of the magnetic layer in the circumferential direction can be enhanced and crystal magnetic anisotropy constant (Ku) can be improved. Therefore, it is possible to improve magnetic characteristics such as the coercive force, the S/N ratio of the recording and reproduction signal, and thermal stability.
In addition, in the present invention, due to antiferromagnetic bonding between magnetic films, regarding the magnetization of the magnetic films other than the primary magnetic film which has the highest coercive force, it is possible to achieve a state wherein there is no apparent magnetization, or a state wherein the magnetization of the primary magnetic film is apparently reduced by an amount of magnetization corresponding to the magnetization of the magnetic films other than that of the primary magnetic film.
Therefore, the volume of the magnetic grains can be increased sufficiently without adversely affecting noise and resolution, thermal stabilization can be attained, and thermal stability can be improved.
The magnetic layer may have a laminated ferrimagnetic structure in which the directions of the magnetic moments of adjacent magnetic films are opposite to each other.
The magnetic layer may have a structure including a plurality of magnetic films and an intermediate film provided therebetween.
The magnetic layer may have two or more laminated structures, each including a magnetic film and an intermediate film adjacent thereto.
Preferably, the antiferromagnetic bonding magnetic field of a magnetic film adjacent to the primary magnetic film having the largest coercive force among the plurality of magnetic films is set to be larger than the coercive force of the magnetic film adjacent to the primary magnetic film.
Preferably, the intermediate film is formed from a material predominantly comprising at least one element selected from among Ru, Cr, Ir, Rh, Mo, Cu, Co, Re, and V.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution formed of one or more elements selected from among Cr, V, Nb, Mo, W, and Ta.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution formed of an alloy predominantly comprising Cr.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution predominantly containing a Ta-containing alloy X1Ta (wherein X1 is one or more elements selected from among Be, Co, Cr, Fe, Nb, Ni, V, Zn, and Zr), and may have an Fd3m structure or an amorphous structure.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution predominantly containing an Nb-containing alloy X2Nb (wherein X2 is one or more elements selected from among Be, Co, Cr, Fe, Ni, Ta, V, Zn, and Zr), and may have an Fd3m structure or an amorphous structure.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution predominantly containing CoTa (Ta content: 30-75 at %) or CoNb (Nb content: 30-75 at %), and may have an Fd3m structure or an amorphous structure.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution predominantly containing CrTa (Ta content: 15-75 at %) or CrNb (Nb content: 15-75 at %).
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution predominantly containing NiTa (Ta content: 30-75 at %) or NiNb (Nb content: 30-75 at %), and may have an Fd3m structure or an amorphous structure.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution containing a non-magnetic metal having an Fd3m structure.
The orientation-adjustment layer may have a constitution which causes the non-magnetic undercoat layer of a bcc structure to have a predominant orientation plane of (200), i.e., a constitution containing a non-magnetic metal having a C15 structure.
In the present invention, an orientation-enhancing layer may be formed between the non-magnetic substrate and the orientation-adjustment layer.
The orientation-enhancing layer may comprise a material having a B2 structure or an amorphous structure.
The orientation-enhancing layer may predominantly comprise any one of NiAl, FeAl, CoAl, CoZr, CoCrZr, and CoCrC.
In the present invention, a plurality of orientation-adjustment layers may be provided.
The magnetic recording medium of the present invention adopts a constitution which has a basic structure of a non-magnetic substrate, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein an orientation-adjustment layer for adjusting the crystal orientation of a layer provided directly thereon is formed between the non-magnetic substrate and the magnetic layer; the magnetic layer has a crystal structure in which columnar fine crystal grains are inclined in the circumferential direction; and the ratio of the coercive force in the circumferential direction of the magnetic layer Hcc to the coercive force in the radial direction of the magnetic layer Hcr, i.e., Hcc/Hcr, is more than 1.
The magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and a structure in which it is possible to form antiferromagnetic coupling between the magnetic films is preferable.
The orientation-adjustment layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
The magnetic recording medium of the present invention assumes a constitution having a basic structure of a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein an orientation-adjustment layer for adjusting the crystal orientation of a layer provided directly thereon is formed between the non-magnetic substrate and the non-magnetic undercoat layer; the non-magnetic undercoat layer has a bcc structure; the magnetic layer has a crystal structure in which columnar fine crystal grains are inclined in the circumferential direction; the orientation-adjustment layer is formed from an NiP alloy having an amorphous structure, and can cause the non-magnetic undercoat layer to have a predominant orientation plane of (200); and the ratio of the coercive force in the circumferential direction of the magnetic layer Hcc to the coercive force in the radial direction of the magnetic layer, (Hcr), i.e., Hcc/Hcr, is more than 1.
The non-magnetic undercoat layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
The magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and a structure in which it is possible to form antiferromagnetic coupling between the magnetic films is preferable.
The orientation-adjustment layer may comprise nitrogen or oxygen in an amount of at least 1 at %.
The magnetic recording medium production process of the present invention produces a magnetic recording medium which takes as a basic structure a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein the non-magnetic undercoat layer has a bcc structure, and an orientation-adjustment layer for causing the non-magnetic undercoat layer to have a predominant orientation plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; and is characterized in that the magnetic layer is formed by releasing film formation particles from a release source and depositing them on a deposition surface, and at this time, the direction of the film formation particles is set so that the projection line of the film formation particle trajectory to a surface perpendicular to the radial direction of the film formation particle deposition point is inclined with respect to the non-magnetic substrate.
In the production method of the present invention, the magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and a structure in which it is possible to form antiferromagnetic coupling between the magnetic films is preferable.
In the production process of the present invention, it is possible to form at least one of the non-magnetic undercoat layer and the orientation-adjustment layer, and at that time, to set the film formation particles such that a projection line to the deposition surface of the trajectory of the film formation particles lies substantially along the radial direction of the non-magnetic substrate and impinges at an angle with respect to the non-magnetic substrate.
In the production process of the present invention, it is possible to carry out oxidation or nitrification on the orientation-adjustment layer.
The orientation-adjustment layer may be formed through sputtering by use of a sputtering target serving as a release source of film formation particles.
When the orientation-adjustment layer is formed, an oxidation process or nitrification process by use of a sputtering gas containing oxygen or nitrogen may be carried out.
The oxidation process or nitrification process may be carried out by bringing the surface of the orientation-adjustment layer into contact with an oxygen-containing gas or a nitrogen-containing gas.
The production apparatus for producing a magnetic recording medium of the present invention is an apparatus for producing a magnetic recording medium having a basic structure of a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein the non-magnetic undercoat layer has a bcc structure, and an orientation-adjustment layer for causing the non-magnetic undercoat layer to have a predominant orientation plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; the apparatus comprises a release source for forming a magnetic layer by releasing film formation particles and depositing the particles onto a deposition surface, and a direction-setting means for setting the direction of the film formation particles released from the release source, and is characterized in that the direction-setting means can set the direction of the particles such that a projection line of the trajectory of the formation particles to a surface which is perpendicular to the radial direction of the film formation particle deposition point is at an angle with respect to the non-magnetic substrate.
The magnetic recording and reproducing apparatus of the present invention provides a magnetic recording medium, and a magnetic head for recording information onto the magnetic recording medium and reproducing the data therefrom, and is characterized in that the magnetic recording medium has a basic structure of a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein the non-magnetic undercoat layer has a bcc structure; an orientation-adjustment layer for causing the non-magnetic undercoat layer to have a predominant orientation plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; the magnetic layer has a crystal structure in which columnar fine crystal grains are inclined in the circumferential direction; and the ratio of the coercive force in the circumferential direction of the magnetic layer Hcc to the coercive force in the radial direction of the magnetic layer Hcr; i.e., Hcc/Hcr, is more than 1.
The non-magnetic undercoat layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
The magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and a structure in which it is possible to form antiferromagnetic coupling between the magnetic films is preferable.
The orientation-adjustment layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.